1. Field of the Invention
The present invention relates to an organic light emitting display device (OLED) and, more particularly, to an emission driver for an OLED.
2. Discussion of the Background
An OLED is a light-emissive display that supplies a scan signal to selected pixels and supplies a data signal to pixels selected by the scan signal so that driving current supplied to an organic light emitting diode in a pixel can be controlled. Whether driving current is supplied to an organic light emitting diode is determined by an emission control signal. The emission control signal is supplied from an emission driver to the pixels.
An emission driver supplies an emission control signal to an active matrix-type pixel in an OLED. A data signal is transmitted to the pixel through a data line, and driving current corresponding to the data signal is supplied to an organic light emitting diode in the pixel in response to the emission control signal. Thus, the emission control signal controls the organic light emitting diode's light characteristics, including intensity and duration.
Each pixel includes an active circuit to store the data signal and to control a light-emission operation in response to the emission control signal. The active circuit can include PMOS transistors, which is common, or NMOS transistors, but all transistors of the active circuit generally have the same conductivity type.
Also, the emission driver may be formed on a single crystalline silicon substrate or on the same substrate as the OLED. When the emission driver is formed on a single crystalline silicon substrate, the emission driver generally uses CMOS transistors to minimize the power consumed during operation. However, when the emission driver is formed on the same substrate as the OLED, the emission driver includes all transistors of either PMOS or NMOS type, and power consumption increases as a result.
An emission driver typically includes a shift register with an arrangement of flip-flops, and data stored in a flip-flop is transmitted to a subsequent flip-flop coupled together in synchronization with a clock signal.
Examples of a shift register are disclosed in Japanese Laid-Open Publication No. 2001-083941, Japanese Patent No. 1994-138838, and Japanese Laid-Open Publication No. 2004-152482.
Japanese Laid-Open Publication No. 2001-083941 discloses a shift register used for a liquid crystal display device (LCD), and the shift register has a structure to prevent a reduction in contrast. Also, a shift register for an LCD, proposed by Japanese Patent No. 1994-138838, is directed to reducing power consumption and shortening the time required to transmit signals. Further, a shift register for an LCD, in which the shift register can change the pulse width of an output signal, is disclosed in Japanese Laid-Open Publication No. 2004-152482. However, the scope of the above-described shift registers, provided to transmit scan signals to LCDs, are restricted to use with LCDs and do not teach similar applications to OLEDs.